Rail car systems having both friction and dynamic brakes have been known for some time, and numerous attempts have been made to achieve a proper blending of the friction and dynamic braking efforts. U.S. Pat. No. 3,536,360 for Blending Scheme for Fluid-Operated and Dynamic Brakes, assigned to the assignee of this application, shows a number of prior art solutions to this problem, wherein brake signals are pneumatically relayed through the train. The prior art also teaches the concept of rail car brake systems wherein a brake application or release signal is conducted through the train by electrical wires rather than pneumatic conduits. In such instances, numerous attempts have been made to achieve a reliable transformation of the electrical signal into a fluid pressure brake application. Examples of such prior art systems are shown in U.S. Pat. No. 3,528,709 for Electric Current-to-Pneumatic Pressure Transducer, and U.S. Pat. No. 3,536,361 for Blending Scheme for Current Responsive Railway Brake, also assigned to the assignee of this application.
While the prior art devices have achieved a significant measure of success, significant drawbacks have been experienced. In the patented systems just mentioned, substantial air pressure losses have been experienced on long trains through the large number of pneumatically piloted supply and exhaust valves. Moreover, the response times of the prior art devices have been relatively long, which has diminished their acceptability for use in some applications. Finally, the pneumatic portions of the prior art systems have generally been rather complex and difficult to maintain in the required working order to minimize leakage losses and response times.